Pneumatic tire for passenger car

ABSTRACT

In a pneumatic tire of the type which consists of a pair of right and left beads, a pair of right and left side walls continuing the beads, respectively, and a tread interposed between the side walls, and in which a carcass cord layer is spread between the beads, and at least two layers consisting of a belt reinforcing layer whose reinforcing cords have a cord angle of from 15° to 30° with respect to the circumferential direction of the tire and a belt reinforcing layer whose reinforcing cords have a cord angle of from 150° to 165° with respect to the tire circumferential direction, and laminated and disposed between the tread and the carcass cord layer, a pneumatic tire for a passenger car characterized in that the carcass cord layer has a two-layered laminate structure consisting of upper and lower carcass cord layers; the angle of the reinforcing cords constituting each of the carcass cord layers with respect to the tire circumferential direction, when measured from the side in which the angle of the reinforcing cords of the belt reinforcing layer on the contact side with the carcass cord layer describes an acute angle with respect to the tire circumferential direction, is such that the mean value 1/2(α 1  +α 2 ) of the angle α 2  of the reinforcing cords of the carcass cord on the contact side with the belt reinforcing layer and the angle α 1  of the reinforcing cords of the carcass cord layer below the former is from 96° to 108° and their difference (α 2  -α 1 ) is from 10° to 40°; the upper carcass cord layer consists of polyester while the lower carcass cord layer consists of nylon; both ends of the upper carcass cord layer are extended from the ends of the belt reinforcing layers to the bead wires of the beads while both ends of the lower carcass cord layer are turned up from inside to outside by the bead wires; and the surface creep distance x of the upper carcass cord layer from the end of the belt reinforcing layer to the end thereof and the surface creep distance l of the lower carcass cord layer from the end of the belt reinforcing layer to the upper end of the bead wire satisfy the relation x/l=0.2˜0.9.

BACKGROUND OF THE INVENTION

This invention relates generally to a pneumatic tire, and moreparticularly to a pneumatic tire for a passenger car which reduces plysteer of the tire to improve straight driving performance anddrastically improve running stability and drastically, durability inhigh speed running, and which is light in weight and economical.

A radial tire for a passenger car in accordance with the prior artgenerally has a construction in which a belt reinforcing layerconsisting of at least two layers is interposed between a tread and acarcass cord layer. Reinforcing cords of one of these belt reinforcinglayers have a cord angle of from 15° to 30° with respect to thecircumferential direction of the tire while the reinforcing cords of theother have a cord angle of from 150° to 165° with respect to the tirecircumferential direction, and these reinforcing cords cross oneanother. The carcass cord layer consists of one or two layers, and thecords of each layer are disposed at an angle of about 90° with respectto the tire circumferential direction. In comparison with a bias tire,the radial tire of this kind is more excellent in the aspects of brakeperformance, low fuel consumption and wear resistance due to the effectbrought forth by the belt reinforcing layers, but has a problem in thatrunning stability is lower due to the belt reinforcing layers. In otherwords, when the radial tire rotates and advances, a lateral force occurseither to the right or left to the advancing direction, even if a slipangle is zero, so that a car advances in a direction different from thedirection in which the driver of the car wishes to drive the car.

Generally, the lateral force with the zero slip angle consists of forcecomponents resulting from two different mechanisms. One is called"conicity" (CT) with the other being called "ply steer" (PS), and theyare classified as part of the uniformity characteristics of the tire. Onthe other hand, in accordance with a uniformity test method (JASO C607)for a car tire, the conicity CT and the ply steer PS are expressed bythe following equation from their definition where LFD represents themean value of the lateral force when the tire rotates once, LFDwrepresents the value when measured on the face and LFDs represents thevalue when measured on the reverse by changing the position of the tire:

    LFDw=PS+CT                                                 (1)

    LFDs=PS-CT                                                 (2)

PS and CT can be obtained as follows from equation (1) and (2): ##EQU1##

Each relation between (1) through (4) is illustrated in FIG. 1.

Among the conicity and the ply steer described above, the conicity isbelieved to be a force that is generated because the tire shape isgeometrically asymmetric with respect to the center of thecircumferential direction of the tire, that is, a force that isgenerated when the tire assuming the shape of a circular truncated conerolls. The main reason for the occurrence of this force is the positionof the belt reinforcing layer inserted into the tread of the tire, andhence can be reduced by somehow improving the production procedures. Incontrast, the ply steer is a force that is inherent to the structure ofthe belt reinforcing layer, and can not be drastically reduced inpractice unless the structure itself of this belt reinforcing layer ischanged.

Let's consider the belt reinforcing layer. The belt reinforcing layercan be expressed as a two-layered laminate sheet 50 consisting of beltreinforcing layers 50u and 50d, as depicted in FIG. 2(A). It is wellknown in the art that when a tensile force is caused to act upon thistwo-layered laminate sheet 50 in the tire circumferential direction EE',the two-layered laminate sheet 50 undergoes not only deformation insidethe two-dimensional plane on which the tensile force acts but also twistdeformation three-dimensionally of the plane as depicted in FIG. 2(B).The ply steer described above results from this twist deformation of thebelt reinforcing layer.

Various proposals have been made in the past so as to reduce the plysteer by adding a new belt reinforcing layer to the existing beltreinforcing layer, but the addition of the new belt reinforcing layer isnot much desirable because it deteriorates the characterizing featuresof the radial tire such as its low fuel consumption, and the like.

The inventors of the present invention made intensive studies in orderto eliminate the problem described above, and as a result, proposedpreviously a pneumatic tire (Japanese Patent Laid-Open No. 114704/1982).In the pneumatic tire of this prior patent application which is equippedwith the belt reinforcing layer of the structure described above andwith a carcass cord layer consisting of upper and lower two layers, theangle of reinforcing cords constituting each carcass cord layer withrespect to the tire circumferential direction, when measured from theside in which the reinforcing cords of the belt reinforcing layer on thecontact side with the carcass cord layer describe an acute angle withrespect to the tire circumferential direction, is such that the meanvalue 1/2(α₁ +α₂) of the angle α₂ of the reinforcing cords of thecarcass cord on the contact side with the belt reinforcing layer and theangle α₁ of the reinforcing cords of the carcass cord below the formeris from 96° to 108° and their difference (α₂ -α₁) is from 10° to 40°.According to this arrangement, the ply steer can be reduced withoutadding afresh any belt reinforcing layer, and running stability due tothe belt reinforcing layer can be improved drastically.

However, when the reinforcing cords of each carcass cord layer arearranged to cross one another at a predetermined angle in the tirecircumferential direction in order to improve the running stability asdescribed above, another problem develops in that the reinforcing cordsof each carcass cord layer are cut due to compression, particularly whendriving at a low internal pressure of the tire.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide apneumatic tire for a passenger car which eliminates the problemdescribed above, improves the running stability, can drastically improvethe durability particularly when driving at a low internal tirepressure, and is light in weight and economical.

In a pneumatic tire of the type which consists of a pair of right andleft beads, a pair of right and left side walls continuing from thebeads, respectively, and a tread interposed between the side walls, andin which a carcass cord layer is spread between the beads, and at leasttwo layers consisting of a belt reinforcing layer whose reinforcingcords have a cord angle of from 15° to 30° with respect to thecircumferential direction of the tire and a belt reinforcing layer whosereinforcing cords have a cord angle of from 150° to 165° with respect tothe circumferential direction of the tire, are laminated and disposedbetween the tread and the carcass cord layer, the pneumatic tire for apassenger car to accomplish the object of the invention described abovehas a construction in which the carcass cord layer has a two-layeredlaminate structure consisting of upper and lower carcass cord layers;the angle of reinforcing cords constituting each carcass cord layer withrespect to the tire circumferential direction, when measured from theside in which the angle of the reinforcing cords of the belt reinforcinglayer on the contact side with the carcass cord layer describes an acuteangle with respect to the tire circumferential direction, is such thatthe mean value, 1/2(α₁ +α₂), of the angle α₂ of the reinforcing cords ofthe upper carcass layer with respect to the tire circumferentialdirection and the angle α₁ of the reinforcing cords of the lower carcasslayer with respect to the tire circumferential direction is from 96° to180° and their difference (α₂ -α₁) is from 10° to 40°; the upper carcasscord layer consists of polyester while the lower carcass cord layerconsists of nylon; both ends of the upper carcass cord layer areextended from the ends of the belt reinforcing layers to the bead wiresof the beads while both ends of the lower carcass cord layer are turnedup from inside to outside by the bead wires; and the surface creepdistance x of the upper carcass cord layer from the end of the beltreinforcing layer to the end thereof and the surface creep distance l ofthe lower carcass cord layer from the end of the belt reinforcing layerto the upper end of the bead wire satisfy the relation x/l=0.2˜0.9.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the relation between the driving distanceand the lateral force of a radial tire;

FIGS. 2(A) and 2(B) are model views showing the state of deformation ofa belt reinforcing layer;

FIG. 3 is a semi-sectional perspective view showing an example of theconventional pneumatic tire;

FIGS. 4 and 5 are semi-sectional perspective views showing an example ofthe pneumatic tire in accordance with the present invention;

FIG. 6 is a transverse sectional schematic view showing the right halfof an example of the pneumatic tire of the present invention;

FIG. 7 is an exploded plan view of the belt reinforcing layer andcarcass cord layer of the tire shown in FIG. 6;

FIG. 8 is also an exploded plan view of another example of the pneumatictire of the present invention;

FIG. 9 is a diagram showing the relation between the ply steer and amean angle value β;

FIG. 10 is a diagram showing the relation between the ply steer and anangle difference (α₂ -α₁); and

FIG. 11 is a diagram showing the relation between durability in highspeed running and the mean angle value β.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the construction of the present invention will be describedin detail with reference to one embodiment thereof shown in theaccompanying drawings.

FIG. 3 is a semi-sectional perspective view of a pneumatic tire inaccordance with the prior art. In the drawing, reference numeral 1represents a tread and reference numeral 2 represents side walls thatextend from both sides of the tread 1. Reference numeral 3 representsbead wires embedded into the lower end portions of the side walls alongthe circumferential direction. A carcass cord layer 4 is disposed insuch a manner as to wrap the bead wires 3 at both end portions and toextend along the inner surfaces of the side walls and the inner surfaceof the tread 1. A belt reinforcing layer 5 having steel cords isinterposed between the carcass cord layer 4 and the tread 1. The carcasscord layer 4 has a two-layered laminate structure consisting of an uppercarcass cord layer 4u and a lower carcass cord layer 4d, and the beltreinforcing layer 5 has also a two-layered laminate structure consistingof an upper belt reinforcing layer 5u and a lower belt reinforcing layer5d.

Among the two layers that constitute the belt reinforcing layer 5, thecord angle of the reinforcing cords of the upper belt reinforcing layer5u is from 150° to 165° with respect to the tire circumferentialdirection EE', and the cord angle of the reinforcing cords of the lowerbelt reinforcing layer 5d is from 15° to 30° with respect to the tirecircumferential direction. The reinforcing cords of the upper and lowerbelt reinforcing layers 5u, 5d cross one another.

In the pneumatic tire such as shown in FIG. 3, the present inventionparticularly stipulates the carcass cord layer. This embodiment will bedescribed with reference to FIGS. 4 through 8. FIGS. 4 and 5 aresemi-sectional perspective views of the pneumatic tire in accordancewith the present invention, FIG. 6 is a transverse sectional view of theright half of the pneumatic tire, and FIGS. 7 and 8 are exploded planviews of the belt layers and carcass cord layers of the pneumatic tire.

(1) The cord angle of the reinforcing cords constituting the carcasscord layer 4 with respect to the tire circumferential direction is oneof the important factors to reduce the ply steer. Therefore, the cordsmust be arranged so as to satisfy the following condition.

The cord angles of the reinforcing cords of the upper and lower carcasscord layers 4u, 4d forming the carcass cord layer 4 with respect to thetire circumferential direction are measured from the side in which thereinforcing cords of the lower belt reinforcing layer 5d on the contactside with the carcass cord layer 4 describes an acute angle with respectto the tire circumferential direction. The mean value β=1/2(α₁ +α₂) ofthe angle α₁ of the reinforcing cords of the lower carcass cord layer 4dand the angle α₂ of the reinforcing cords of the upper carcass layer 4umust be from 96° to 108°, while their difference (α₂ -α₁) must be from10° to 40°. Since these angles α₁ and α₂ are measured from the side inwhich the reinforcing cords of the lower belt reinforcing layer 5d onthe contact side with the carcass cord layer 4 describe an acute anglewith respect to the tire circumferential direction EE', they must bemeasured clockwise in the rotating direction with respect to the tirecircumferential direction EE', if the reinforcing cords of the lowerbelt reinforcing layer 5d are arranged leftwardly downward as shown inFIG. 8.

As is obvious from the relation of the angles α₁ and α₂ described above,the reinforcing cords of the upper carcass cord layer 4u must bedisposed so that their cord angle α₂ is greater than that α₁ of thereinforcing cords of the lower carcass cord layer 4d and moreover, theycross one another. Since the mean value β of these angles α₁ and α₂ isfrom 96° to 108°, the ply steer that results from the twist deformationof the belt reinforcing layer 5 can be reduced without adding afresh anybelt reinforcing layer, the running stability of the tire can beimproved. The handling and stability is enhanced.

If β is below 96°, the ply steer can not be much improved when comparedwith that of the conventional radial tire, and if it is above 108°, theply steer can be further improved, it is true, but drivingcomfortability drops to a level lower than that of the conventionalradial tire. Even if the mean value β is within the range of from 96° to108°, however, the difference (α₂ -α₁) must be from 10° to 40°. If thedifference (α₂ -α₁) is from 10° to 40°, the rigidity at the carcassportion can be improved in comparison with a so-called radial tire inwhich two-layered carcass cord layers are disposed parallel in the tiresectional direction, and higher handling and higher stability can beenjoyed. If the difference (α₂ -α₁) is below 10°, the carcass rigiditybecomes insufficient and the handling and stability drops undesirably.If the difference (α ₂ -α₁) is above 40°, the durability in heavy loadrunning drops, although the ply steer can be improved.

(2) The upper carcass cord layer 4u is made of polyester, while thelower carcass cord layer 4d is made of nylon. If these materials areused respectively, the ply steer can be reduced drastically anddurability in high speed running can be improved remarkably. If thecarcass cord layers are made of synthetic fibers other than polyesterand nylon, the balance of the heat shrinkage ratios between the lowerand upper carcass cord layers drops and the effects described above cannot be much observed.

(3) Both ends of the upper carcass cord layer 4u are positioned betweenthe ends of the belt reinforcing layer 5 (at the end of 5d in FIG. 6)and the bead wires 3 of the beads, while both ends of the lower carcasscord layer 4d are turned up from inside to outside by the bead wires.

The arrangement described above is employed for the following reason.The respective carcass cord layers are made of polyester and nylon asdescribed in the item (2) above, and when the carcass angle beforevulcanization and after vulcanization is measured so as to compare thechange, it is confirmed that the change quantity of the upper carcasscord layer is greater by about 5° to about 10° than that of the lowerone 4d. This means that a greater tensile force acts upon the carcasscord of the upper carcass cord layer than upon that of the lower carcasscord layer. If polyester is used for the upper layer and nylon is usedfor the lower layer, the nylon cord is apt to break along the polyestercord and can not withstand the practical use particularly when theinternal tire pressure is low or when an excessive load is applied tothe tire, because the modulus of polyester is higher than that of nylon.The carcass cord layers 4u and 4d are disposed as described above inorder to control the difference of this tensile force. This arrangementmakes it possible to provide a light-weight and economical pneumatictire.

(4) The surface creep distance x of the upper carcass cord layer 4u fromthe end of the belt reinforcing layer 5 (at the end of 5d in FIG. 6) tothe end of the upper carcass cord layer 4u must be set so as to satisfythe relation x/l=0.2˜0.9 with respect to the surface creep distance l ofthe lower carcass cord layer 4d from the end of the belt reinforcinglayer 5 to the upper end of the bead wire 3.

If this ratio x/l is below 0.2, reduction of the ply steer andimprovement in durability in high speed running can not be accomplishedsufficiently. If x/l is about 0.9, however, not only the reduction ofthe tire weight becomes insufficient but also various problems such asvulcanization trouble and difficulty in tire molding occur because theend of the upper carcass cord layer 4u is too close to the bead wire 3.

In the embodiment described above, the belt reinforcing layer 5 has atwo-layered laminate structure made of the steel cords. However, variousother belt reinforcing layers can also be used in the present invention.For example, a two-layered laminate structure consisting of a beltreinforcing layer of steel cords and a belt reinforcing layer ofaromatic polyamide fibers called "KEVLAR" in the trade name, atwo-layered laminate structure consisting of two textile beltreinforcing layers, and so forth, can be used. The end portions of thebelt reinforcing layers may be naturally bent inwards. The presentinvention can also be applied to such a type of a two-layered laminatebelt reinforcing layer to which an additional belt reinforcing layer oftextile cords is added, whenever necessary.

Next, the present invention will be described in further detail with thefollowing definite experimental example thereof.

EXPERIMENTAL EXAMPLE

In a pneumatic tire having the structural form of the invention shown inFIG. 4, various pneumatic tires were produced by keeping the differenceof the cord angles (α₂ -α₁) of the upper and lower carcass cord layersconstant at 30°, but changing variously the mean angle value β withinthe range of from 90° to 114°. The cord angles of the upper and lowerbelt reinforcing layers with respect to the tire circumferentialdirection were 20° and 160°, respectively. The tire size was 195/70HR14and the rim was 51/2-JJ×14. The ply steer of these pneumatic tires wasmeasured in accordance with the uniformity test method JASO C607 for apassenger car, with the results shown in FIG. 9. In FIG. 9, symbol ○represents the result of the conventional pneumatic tire (JapanesePatent Laid-Open No. 114704/1982) and symbol represents the results ofthe pneumatic tires of the present invention.

Similarly, FIG. 10 illustrates the results of an experiment in which themean value β of the cord angles of the upper and lower carcass cordlayers was kept constant at 102° but the difference (α₂ -α₁) of thesecord angles were changed variously within the range of from 10° to 40°.Symbols ○ and have the same meaning as described above.

Next, a durability in high speed running test was conducted for each ofthe tires used in the experiments shown in FIGS. 9 and 10 using anindoor drum tester consisting of a drum of a 1707 mm diameter. Eachpneumatic tire was placed under the condition of an air pressure of 2.1kg/cm², a load of 550 kg and an initial speed of 81 km/hr. The speed wasincreased by 8 kg/hr every 30 minutes and was caused to run until it wasbroken. The speed at that time was compared with the speed of theconventional tire (Japanese Patent Laid-Open No. 114704/1982) which wasindexed as 100%. The result was plotted in terms of percentage as shownin FIG. 11.

It can be understood clearly from FIGS. 9 through 11 that the pneumatictire in accordance with the present invention was found superior to theconventional pneumatic tire in the aspects of running stability anddurability in high speed running.

As described above, the present invention reduces the ply steerresulting from the belt reinforcing layer in comparison with theconventional pneumatic tire, and improves running stability and drivingcomfortability. Moreover, the present invention improves also thehandling and stability as well as durability in high speed running incomparison with the conventional pneumatic tire. Furthermore, thepresent invention can provides a light-weight economical pneumatic tire.

What is claimed is:
 1. In a pneumatic tire comprising a tread, sidewalls extending from both sides of said tread and containing bead wires,a carcass cord layer and at least two belt reinforcing layers disposedbetween said tread and said carcass cord layer, reinforcing cord of oneof said belt reinforcing layers having an angle of 15 to 30 degrees withrespect to tire circumferential direction and reinforcing cord of saidother belt reinforcing layer having an angle of 150 to 165 degrees withrespect to tire circumferential direction and said carcass cord layercomprising a laminate of upper and lower carcass cord layers and theaverage value 1/2(α₁ +α₂) of the angle α₂ of reinforcing cord of saidupper carcass cord layer adjacent said belt reinforcing layers withrespect to tire circumferential direction and the angle α₁ ofreinforcing cord of said lower carcass cord layer with respect to tirecircumferential direction is from 96 to 108 degrees and their difference(α₂ -α₁) is from 10 to 40 degrees when measured from the side in whichthe angle of the reinforcing cords of said belt reinforcing layeradjacent said carcass cord layer describes an acute angle with respectto the tire circumferential direction; the improvement comprising saidupper carcass cord layer comprising polyester and said lower carcasscord layer comprising nylon with both ends of said upper carcass cordlayer extending from both ends of said belt reinforcing layer towardsaid bead wires but not being turned up around said bead wires and bothends of said lower carcass cord layer being turned up from inside tooutside around said bead wires and surface creep distance x of saidupper carcass cord layer from the end of said belt reinforcing layer tothe end thereof and the surface creep distance l of said lower carcasscord layer from the end of said belt reinforcing layer to the upper endof said bead wire satisfy the relation x/l=0.2˜0.9.
 2. The tire of claim1 wherein said belt reinforcing layers are a two-layered laminatestructure having steel cords.
 3. The tire of claim 1 wherein said beltreinforcing layers comprise a layer having steel cords and a layerhaving aromatic polyamide fibers.
 4. The tire of claim 1 wherein saidend portions of said belt reinforcing layers are bent inwardly.